Nuclear Detonations in Space: Reducing Risks to Low Earth Orbit Satellites

On July 9, 1962, just after 11 PM, the dark, cloudy summer night above Honolulu turned to day for six minutes. A brilliant flash lit up the sky, shifting from green to yellow to a lingering red. The United States had just detonated a 1.4 megaton W49 thermonuclear warhead 250 miles above the Johnston Atoll. 

“Starfish Prime” was neither the first nor last U.S. or Soviet nuclear test in space, but it was the first to clearly show the consequences of a high-altitude nuclear detonation (HAND). In addition to knocking out hundreds of streetlights over 825 miles away on the ground in Honolulu, the blast’s resulting electromagnetic pulse (EMP) subjected satellites in its line of sight to instant, severe radiation damage. What became clear later is that the blast artificially increased the intensity of the Earth’s naturally occurring inner and outer Van Allen radiation belts through the early 1970s. These effects damaged or destroyed a third of existing low-earth orbit (LEO) satellites within seven months.

Starfish Prime inspired treaties in 1963 and 1967 barring nuclear weapons use in space, but U.S. policymakers should not be lulled into complacency today by the existence of these agreements. As relations with space rivals such as Russia and China deteriorate, a HAND first strike may appear increasingly tempting in a future crisis, given the considerable military advantages the United States derives from satellites in orbit. The United States should develop a more resilient LEO satellite infrastructure to reduce the expected gains adversaries hope to achieve with a nuclear first strike in space. This deterrence by denial should make a space-based nuclear detonation—and its harmful consequences—less likely.

Threats to U.S. Space Infrastructure

The United States derives too many advantages, from intelligence collection to the command, control, and communications (C3) capabilities satellites provide, to not anticipate that adversaries might attempt to degrade U.S. space-based infrastructure in future conflicts.

Several countries have developed and are improving their ability to attack satellites. In addition to the United States, Russia, China, and India have tested direct-ascent anti-satellite (DA-ASAT) missiles, which are conventional munitions that launch from Earth and intercept satellites in orbit. These strikes are widely opposed (for instance, the United States has adopted a moratorium on its own DA-ASAT tests since 2022) because they threaten humanity’s future access to space. For example, China’s first successful 2007 ASAT test created the largest-ever debris field in space, yielding over 3,000 trackable objects that still endanger the International Space Station more than a decade and a half later.

Russia and China have tested or are seeking to develop a variety of other conventional ASAT capabilities that carry fewer risks to their use of space. Kinetic options include ground-based or submarine-mounted ASAT lasers capable of blinding or destroying satellites and co-orbital attacks in which satellites already in orbit steer into the path of enemy satellites and destroy them with explosives or physically grapple and de-orbit them. Adversaries can also pursue a variety of non-kinetic ASAT options, such as jamming or spoofing satellites’ signals, or sabotaging or even commandeering satellites through cyberattacks.

As U.S. launch costs shrink and satellite constellations trend toward greater numbers of more replaceable platforms, individual satellites matter less, and therefore conventional ASAT strikes offer adversaries fewer rewards. This calculus may not hold for HAND strikes.  Earlier this year, troubling news broke that Russia is developing an anti-satellite nuclear weapon. Little information is publicly known about the Russian program or how close it is to deployment. During his testimony in  May 2024, then-Assistant Secretary of Defense for Space Policy, John F. Plumb told Congress that Russia’s plans would involve Russia launching a nuclear weapon-equipped satellite into orbit that could inflict indiscriminate damage to other nations’ satellite infrastructure if employed. 

High Risks, Intractable Challenges

A high-altitude nuclear detonation could prove surprisingly difficult to deter through traditional means. If Vladimir Putin does conclude that nuclear escalation in Ukraine is necessary, he might favor a detonation in space instead of a demonstration strike over the Black Sea or a tactical strike on Ukrainian forces. A HAND strike is still a nuclear detonation with the appropriate demonstrative value. Yet it does not produce fallout which may also put Russia at risk. Further, as HAND strikes disable satellite communication, Russia could knock out Ukraine’s and its supporters’ access to space-based communication networks such as Starlink. This may afford Russia battlefield advantages, in addition to the psychological impact. 

The combination of high effect, low radiation impact, and lack of casualties may incentivize HAND strikes. From the perspective of a U.S. adversary, a space-based nuclear explosion could cause immense damage to an opponent that derives far greater benefit from access to LEO. At the time of Starfish Prime, there were only a few dozen satellites in space. Today, there are over 10,000 satellites in orbit, of which over 90% are in LEO. The United States has a commanding lead, with nearly 3,000 satellites in orbit as of last year, compared to China’s and Russia’s fleets both numbering in the hundreds. Given the disproportionate consequences for the United States, it is not difficult to envision how an increasingly desperate adversary might seek the asymmetric benefits of a HAND.

A HAND strike’s consequences would be daunting. In a prescient 2001 study, the Defense Threat Reduction Agency estimated that even a low-yield nuclear detonation in space could triple or quadruple the radiation in the planet’s Van Allen belts– naturally occurring zones where radiation is trapped by the earth’s magnetic field sitting between 1,000-8,000 miles and 12,000-25,000 miles above the earth’s surface, respectively. The inner Van Allen belt overlaps with the upper edge of low-earth orbit, and as a result, a HAND would cause the vast majority of LEO satellites to fail within a few weeks to two months of detonation due to the increased radiation exposure. The worldwide cost of the strike could amount to  $500 billion in replacement costs alone and up to $3 trillion in overall economic impact. Given its existing space presence—and compounding military and economic dependence on satellites—U.S. costs could be particularly severe. The Bureau of Economic Analysis estimates the U.S. space economy alone comprises at least 0.5 percent of America’s GDP and generates over $232 billion in gross output.

Beyond the economic costs, U.S. military reconnaissance, communications, navigation, and missile warning satellites situated in LEO, such as the Space Development Agency’s planned National Defense Space Architecture Tracking Layer, would all instantly be at risk. In addition to improving the effectiveness of conventional forces, these LEO satellites can aid in the continuous tracking of a range of missile threats, including newer hypersonic warheads operating at lower altitudes. Integrated with a wider constellation of nuclear command, control, and communications (NC3) satellites across all orbits, these early warning satellites collectively provide crucial additional minutes of warning in response to adversary missile launches, offering time for critical decisions about potential countermeasures and personnel evacuations. Unlike NC3 satellites in higher orbits, those in LEO traditionally feature less radiation-hardening because they are typically protected from higher environmental radiation by the Van Allen belts at their normal intensities.

These implications complicate a potential U.S. response to a HAND strike.  If a space-based nuclear strike is a demonstration rather than an opening act to a wider attack, this may warrant a less escalatory response. However, due to the possibly wide-ranging impacts of LEO detonations, it is also difficult to assess the intent of such a strike.  The detonation would cause massive economic damage, ground future satellite launches for over a year or more, and negate key U.S. military advantages, potentially without any death toll. A space-based detonation offers no “in-kind” targets to hold at risk from a traditional “mutually assured destruction” perspective that does not also further damage U.S. prospects of renewed access to space.

Credibly deterring a high-altitude nuclear detonation poses major difficulties. An adversary like Russia may credibly assess that  U.S. policymakers would not be willing to accept the costs of massive conventional retaliation and their associated risks of further nuclear escalation over a non-lethal, predominantly economic attack.

Mitigation Through Innovation

The problems above suggest that deterring a nuclear strike in space through credible threats of punishment is impractical. A better strategy against HANDs is deterrence by denial. Policymakers can make a space-based nuclear detonation less likely to occur by demonstrating to adversaries from the outset that such attacks are less likely to succeed against U.S. LEO satellites.

First, the Department of Defense (DoD) should assign a lead agency to drive research and development (R&D) efforts to develop increasingly cost-effective radiation-hardening capabilities for LEO satellites. The Defense Threat Reduction Agency could be a good choice based on its background in countering nuclear threats. Traditional techniques for radiation-hardening include using heavy metals like lead or tungsten to shield electronic components from charged particles, as well as incorporating redundancies in circuits and other subsystems to reduce the risks of any singular points of failure. At the most expensive end of radiation-hardening, specialized foundries create radiation-insulated semiconductors able to resist high cumulative doses of radiation over long service lives. 

While these additions can significantly increase the costs of individual satellites, the revolutionary cratering of space launch costs over the past several years due to reusable rocket technology could make these safeguards more viable. One estimate suggests that SpaceX’s Starship, which recently completed its first successful launch and recovery, could reduce current launch costs by 50- to 80-fold per kilogram. These cost savings could make more funds available for advanced radiation shielding and satellite resilience measures.

Second, DoD should demonstrate greater willingness to incorporate commercially-produced radiation-hardened components into its LEO satellites when cost and quality standards are met. So far, the Pentagon has made some early progress. The Department issued its first-ever Commercial Space Integration Strategy this year. Earlier in 2024, the Undersecretary of Defense for Research and Engineering also called for industry investment in “rad-hard” electronics. If this proposed initiative is to avoid problems similar to those of  DoD’s drone-focused Replicator Initiative, design choices and procurement decisions that support a private space industry must follow.

Declining launch costs may make investment in hardware resilience a more attractive prospect for private industry. Fortunately, a robust market in radiation-hardening tailored at different levels necessary for the specific mission needs of individual satellites already exists. Redesigns of later tranches of the forthcoming military satellites in LEO, like the National Defense Space Architecture Tracking Layer, offer a prime opportunity to incorporate pre-existing private sector-supplied components that fit mission and cost needs rather than pursuing expensive, bespoke solutions.

Lastly, to create an environment that supports industry risk-taking in areas like radiation-hardening investment, the incoming president should prioritize a regulatory environment that supports a robust U.S. private space industry. Analysts have recognized for decades that commercial space technology is inherently dual-use. The space industry necessarily serves both the civilian market and military purposes. Ground-breaking launch systems like Starship offer the U.S. space industry and the Department of Defense decisively cheaper access to space, reducing the value of conventional anti-satellite attacks by credibly demonstrating the United States’ ability to rapidly redeploy satellite constellations and continue to reap the civil and military benefits of their use. The U.S. government should continue to support innovation in this field, furthering cost reduction and increasing launch capacity. 

In particular, the next president must appoint a Federal Aviation Administration (FAA) head willing to prioritize transparent decision-making processes on commercial space launch licensing with a bias toward rapidly issuing approvals. Unfortunately, since March 2021, FAA commercial launch and reentry regulations, known as Part 450, have made it significantly harder for companies to obtain launch licenses, a barrier highlighted in recent  Senate and House hearings. While the Part 450 regulations, which were developed in 2020, were initially intended to streamline launch approvals, U.S. space industry representatives have argued that the lack of certainty around its implementation creates an essentially bespoke process each time a company seeks a launch license, significantly extending approvals times.   . For example, SpaceX’s first Starship test launch took over 3 years to license. Starship’s first successful landing test in October was subject to months of FAA environmental review delays despite being ready to launch in August. The United States should certainly take pride in having greater regard for its space program’s human and environmental impacts than its rivals do. Regulators can prioritize rapidly processing due diligence checks without overemphasizing the precautionary principle to such a degree that the United States cedes its advantages.

Conclusion

Upgrading existing military LEO satellite constellations through radiation hardening will reduce any adversary’s expected benefits from detonating nuclear weapons in space. Doing so will require supplementing DoD efforts with private innovation to develop new technologies and cut costs for radiation hardening and satellite launches. This is especially pertinent in times of ever more constricted defense budgets. 

A nuclear detonation in space would be devastating for the world collectively and for the United States in particular. While America should make every diplomatic effort to avoid finding itself in a situation where such a strike is likely, it should harden U.S. satellites in LEO to reduce the asymmetric benefits adversaries may imagine they can achieve from a HAND. The Department of Defense has made important partnership strides with the domestic space industry, but other federal agencies like the FAA should also follow suit to create the conditions that can further U.S. strategic goals in space and reduce the potential appeal of a crippling nuclear strike in space.

Views expressed are the author’s own and do not represent the views of GSSR, Georgetown University, or any other entity. Image Credit: SEOS